1. Field of the Invention
The present invention relates to a charging frame for accommodating a batch of parts to be quenched with the aid of a quenching gas, and also relates to a quenching device for quenching the parts, in particular metal workpieces.
2. Description of Related Art
To produce defined workpiece properties, such as a high degree of hardness or a sufficient wear resistance, most metal workpieces are subjected to heat treatment. The speed at which the previously heated workpieces are cooled is important for the treatment result. The use of water, oil or quenching gas is known for the necessary quenching process. The main advantage of using quenching gases instead of quenching liquids is the fact that the parts do not have to be cleaned following quenching as well as the fact that a higher quenching homogeneity within the batch may be achieved. However, to increase the quenching intensity to be achieved with the aid of quenching gas to the extent that this intensity lies in the range of liquids such as quenching oils or molten salt baths, it is necessary to achieve a very high heat transfer between the parts and the quenching gas amounting to more than 3,000 W/m2K, which is possible only at very high flow rates. To achieve the necessary very high flow rates, in turn, the blower used must deliver very high volumetric flows and consequently requires a very high motor output. This is associated with high procurement costs as well as high energy costs during operation. When using blowers having a very high motor output, the problem arises that the pressure loss increases along with an increase in the flow rate within the batch and, as a result, a large part of the quenching gas does not flow through the batch but instead flows past the charging frame accommodating the batch. Thus, the flow rate within the batch; and thus also the quenching intensity, increases very little even though the blower's volumetric flow increases. In addition, conventional charging frames are constructed from gratings which are connected to rods extending in the vertical direction, which makes it possible for additional bypass flows to occur within the batch.
The use of gas nozzle arrays is known from published European patent document EP 0 129 701 B1 and published German utility model application document DE 29 603 022 U1 for increasing the quenching intensity. However, these nozzle arrays have the disadvantage that they produce high flow rates only in the area of the nozzle but not on average over the entire batch.
A quenching device is known from published European patent document EP 1 154 024 B1 in which an adjustable hood which has flow channels is situated in the quenching-chamber, it being possible to pass this hood over the parts accommodated in the charging frame for the purpose of preventing bypass flows. The disadvantage of the known quenching device is its complex construction. To this is added the need to provide moving parts, which are thus also susceptible to wear (hood, adjusting mechanism), in the quenching chamber.